*{
    margin: 0;
    padding: 0;
}
#div1{
    /* border:2px red solid; */
    background-color: red;
    height: 100px;
    width: 100vw;
}

#div2{
    border: 1px blue solid;
    margin: 0 auto;
    height: 100px;
    width: 200px;
}

#div2 p{
    background-color: green;
    height: 30vh;
    width: 30vw;
}
html{
    --fs:20px;
    --fs2:30px
}
#div3{
    font-size: var(--fs3);
}
#div4{
    --fs3:16px;
    font-size: var(--fs2);
}